1. Field of the Invention
The invention described and claimed herein is generally related to fire extinguishing agents. More particularly the present invention is related to halogenated alkane fire extinguishing agents.
2. Background Art
The halogenated fire extinguishing agents are generally alkanes in which one or more hydrogen atoms have been replaced by halogen atoms consisting of fluorine, chlorine, bromine or iodine.
The hydrocarbons from the which halogenated extinguishing agents are derived, for example methane and ethane, are generally volatile and highly flammable gases at room temperature. Substitution of halogens for the hydrogen atoms in such hydrocarbon compounds reduces both the volatility and the flammability of the compound. Sufficient substitution of halogen atoms for hydrogen results in inflammable liquids which are useful as fire extinguishing agents.
Some general observations can be made regarding the relative effects of halogenation of the lower alkanes. Generally, for example, increasing bromine substitution results in increasing boiling point and flame extinguishment properties. Fluorine substitution has much less effect on boiling point, but results in inflammability and lower toxicity than bromine. Chlorine substitution is intermediate between fluorine and bromine. Iodine is rarely utilized because the iodoalkanes are too toxic and unstable.
The use of certain halogenated alkanes as fire extinguishing agents has been known for many years. For example, fire extinguishers containing carbon tetrachloride and methyl bromide were used in aircraft applications as early as the 1920's. Over a period of years the toxicity of these compounds was recognized and they were replaced with less toxic compounds. Chlorobromomethane was used in aircraft applications from the 1950s to the 1970s. A major study of halogenated alkanes as fire extinguishing agents was conducted by the Purdue Research Foundation for the U.S. Army from 1947 to 1950. That study remains the basis for the use of a number of halogenated alkanes in specific fire extinguishing applications.
Further discussion of the halogenated alkanes requires understanding of the two major nomenclature systems that are used in addition to the chemical nomenclature. The "Halon" system was devised by the U.S. Army Corps of Engineers and primarily refers to halogenated alkanes containing bromine and fluorine and used as fire extinguishing agents. In accordance with this system, the first digit of a Halon number refers to the number of carbon atoms; the second digit refers to the number of fluorine atoms in the compound; the third digit refers to the number of chlorine atoms; the fourth digit refers to the number of bromine atoms; and the fifth digit refers to the number of iodine atoms. Terminal zeroes are not expressed. Thus, for example, bromotrifluoromethane (CBrF.sub.3) is referred to as Halon 1301; having one carbon, three fluorines, no chlorines, one bromine and no iodines. Likewise, dibromodifluoromethane is designated Halon 1202.
The chlorofluorocarbon, or "CFC," system of nomenclature was developed primarily with regard to refrigerants, which generally contain chlorine and/or fluorine, and which are generally free of bromine and iodine. Under this system the first digit represents the number of carbon atoms minus one (and is omitted if zero); the second digit represents the number of hydrogen atoms plus one; and the third digit represents the number of fluorine atoms. Unless otherwise indicated, all remaining atoms in the compound are assumed to be chlorine. Thus, for example, CFC 23 represents trifluoromethane (CHF.sub.3).
The 1950 Purdue report resulted in four halons being identified for widespread fire extinguishment use. Halon 1301 (bromotrifluoromethane) was identified as the least toxic and second most effective agent, and consequently has found widespread application as the standard choice in "total flood" applications, which are applications in which the agent is stored and discharged in occupied spaces, such as computer facilities or restaurant kitchens, often by an automatic discharge system. Halon 1211 is more toxic than Halon 1301 and consequently is not used in total flood applications. However, it has has good extinguishment effectiveness, and consequently has become the standard for "streaming" applications, which are those applications where the agent is applied from wheeled or portable units which are manually operated.
The halogenated hydrocarbons operate as fire extinguishing agents by a complex chemical reaction mechanism involving the disruption of free-radical chain reactions. They are desirable as fire extinguishing agents because they are clean and effective; because they leave no residue; and because they do not damage equipment or facilities to which they are applied.
As indicated above, for a number of years the toxicity of the halogenated alkanes has been an issue in their selection as fire extinguishment agents. Even more recently, the ozone depletion potential of halogenated hydrocarbons has come to be recognized. The depletion of ozone in the atmosphere results in increased levels of ultraviolet radiation at the surface of the earth and also contributes to the problem of global warming. These problems are considered so serious that the 1987 Montreal Protocol includes international restrictions on the productions of volatile halogenated alkanes.
Accordingly, it is the object and purpose of the present invention to provide clean, relatively non-toxic, effective fire extinguishing agents which have low ozone depletion potentials.
It is another object and purpose of the present invention to attain the foregoing objects and purposes in fire extinguishing agents which are particularly useful in streaming applications.